When I open the lid of the mac it takes maybe 20-30 seconds to resume. I consider this a small price to pay in exchange for reliable sleep and less battery drain with the lid closed.
If you want to try this, run in the terminal:
sudo pmset -a hibernatemode 25
If you don't like it, you can restore defaults with:
sudo pmset -a hibernatemode 3
SAFE SLEEP ARGUMENTS
hibernatemode supports values of 0, 3, or 25. Whether or not a hibernation image gets
written is also dependent on the values of standby and autopoweroff
For example, on desktops that support standby a hibernation image will be written after the
specified standbydelay time. To disable hibernation images completely, ensure hibernatemode
standby and autopoweroff are all set to 0.
hibernatemode = 0 by default on desktops. The system will not back memory up to persistent
storage. The system must wake from the contents of memory; the system will lose context on
power loss. This is, historically, plain old sleep.
hibernatemode = 3 by default on portables. The system will store a copy of memory to
persistent storage (the disk), and will power memory during sleep. The system will wake from
memory, unless a power loss forces it to restore from hibernate image.
hibernatemode = 25 is only settable via pmset. The system will store a copy of memory to
persistent storage (the disk), and will remove power to memory. The system will restore from
disk image. If you want "hibernation" - slower sleeps, slower wakes, and better battery
life, you should use this setting.
Please note that hibernatefile may only point to a file located on the root volume.